JP-2004-100567A (EP-1538325A1) shows that the ignition timing is detected by a cylinder pressure sensor and a feedback control of the control subject is performed based on the detected ignition timing. More specifically, the heat-release-rate is calculated based on output signals from the cylinder pressure sensor, and then the ignition timing in which the heat-release-rate exceeds a predetermined value is derived. Such a method for detecting the ignition timing is suitable for a combustion mode in which the initial rising inclination is steep. This combustion mode, for example diesel combustion, is referred to as a diffuse combustion.
The cylinder pressure sensor requires a target output characteristic which is shown by a solid line in FIG. 11A. However, due to sensor errors, a gain deviation may be arose as shown by a short dashed line, or an offset deviation may be arose as shown by a long dashed line in FIG. 11A.
When the gain deviation or the offset deviation is arose, the cylinder pressure calculated based on the cylinder pressure sensor output deviates from the actual cylinder pressure as shown in FIG. 11B. A heavy line “A” indicates the actual cylinder pressure, a thin line “B” indicates a calculated cylinder pressure having the gain deviation, the other thin line “C” indicates a calculated cylinder pressure having the offset deviation.
Since the above method for detecting the ignition timing is used for the diffuse combustion in which the initial rising inclination of the heat-release-rate is steep, even when the gain deviation or the offset deviation in output characteristic of the cylinder pressure sensor is arose as shown in FIGS. 12A to 12C and 13A to 13B, a fluctuation of timing in which the heat-release-rate reaches the ignition determination timing is relatively small. Thus, detecting error of the ignition timing is small to accurately detect the ignition timing.
In FIGS. 12A to 12C, heavy lines indicate the gain deviation exists, and thin lines indicate no gain deviation exists. In FIGS. 13A to 13C, heavy lines indicate the offset deviation exists, and thin lines indicate no offset deviation exists.
On the other hand, combustions in engines include not only the diffuse combustion but also a premix combustion such as Homogeneous-Charge Compression-ignition combustion in which the initial rising inclination of the heat-release-rate is gentle. When the method for detecting the ignition timing is applied to the premix combustion, the following problem will arise. That is, when the gain deviation or the offset deviation is arose as shown in FIGS. 12D to 12F and FIGS. 13D to 13F, a fluctuation of timing in which the heat-release-rate reaches the ignition determination timing becomes large. Thus, the detecting error of the ignition timing becomes large. In FIGS. 12D to 12F, heavy lines indicate the gain deviation exists, and thin lines indicate no gain deviation exists. In FIGS. 13D to 13F, heavy lines indicate the offset deviation exists, and thin lines indicate no offset deviation exists.